An investigation into an air crash that killed two men has been unable to determine the reason for the accident.

Pilot Andrew John Sully, 50, from Writtle, and passenger Simon Chamberlain, 29, from Harlow, were both killed when the small plane they were in went to ground in a field off the A414 near Ongar at 2.53pm on March 29 2014, 

They had left North Weald airfield only six minutes earlier after Mr Sully, a senior first officer with British Airways who had 15,000 hours flying experience, notified controllers they were leaving for a “twenty minute local flight”.

A report published today by the Air Accidents Investigation Branch (AAIB) states that five minutes after take-off the 1989 Yak-52 was seen flying at a low level.

The report says: “Having carried out a level turn, the aircraft climbed sharply and entered a stall or spin, from which it did not recover before striking the ground.

“Both occupants received fatal injuries and there was a fire.

“The reason the aircraft was flying at low level and the cause of the final manoeuvre could not be determined.”

The AAIB report considered a number of reasons for the crash, but none were considered conclusive.

Mr Sully was diabetic, but toxicology found he was not hypoglycaemic at the time of the crash.

The aircraft was also found to have been structurally sound at the time and the weather was mostly clear, without strong winds.

The report continued: “The low height at which the aircraft was flying when first noticed by eyewitnesses may indicate that the flight was not proceeding normally.

“It is possible that a problem led to the pilot choosing to descend to low height.

“There was evidence that the engine was running at the moment the aircraft struck the ground but the possibility of a significant loss of engine power could not be discounted.

“No defects were found in those parts of the flying controls that remained but the engineering investigation was hampered by the fact that some components were damaged or destroyed in the post-crash fire.

“The aircraft’s final manoeuvre could not be explained but, having entered a stall or spin, there was little height in which the pilot could regain control before it struck the ground.”